I have a 2004 F-60 4 stroke carbed engine. The problem is when it is cranked cold it starts, idels fine. I run it in the water for 20-30 min and the idle drops so low it stalls. If I adust the idel after it "warms up" it idels way to high when cranked cold. I have tried running it on the hose for an hour and it does not do this. I had the carbs rebuilt recently and carbs were synced. Any suggestions?